1. Field of the Invention
The present invention relates to a pigment-based ink set and a pigment-based yellow ink composition which can realize images having excellent color reproduction and excellent fastness properties.
2. Background Art
Ink jet recording is a printing method wherein droplets of an ink composition are ejected and deposited onto a recording medium, such as paper, to conduct printing. This method has a feature that an image having high resolution and high quality can be printed at a high speed by means of relatively inexpensive apparatuses.
In general, the ink composition used in the ink jet recording comprises water as a main component and, added thereto, a colorant component and a wetting agent, such as glycerin, for preventing clogging and other purposes. A large number of water-soluble dyes have been used as colorants for use in ink compositions for ink jet recording from the viewpoints of high chromas of colorants, an abundance of types of utilizable colorants, solubility in water and the like.
The dyes, however, often have poor lightfastness, waterfastness and other various properties. Therefore, prints obtained using dye ink compositions have poor lightfastness and wasterfastness. The waterfastness has been improved through the use of specialty recording papers having an ink absorptive layer for ink jet recording. For plain papers, however, the improvement in waterfastness is still unsatisfactory.
Pigments, as compared with the dyes, have superior lightfastness and waterfastness. This has recently led to studies on utilization of pigments as colorants in the ink composition for ink jet recording from the viewpoint of improving the lightfastness and waterfastness of printed images. In this case, since pigments are generally insoluble in water, when a pigment is used in a water-based ink composition, a method should be used which comprises mixing the pigment with a resin or the like called a xe2x80x9cdispersantxe2x80x9d to prepare a mixture, stably dispersing the mixture in water, and then preparing an ink composition using the dispersion.
In order to stably disperse pigments in a water system, studies should be made on the kind and particle diameter of pigment, the kind of resin used, dispersing means and the like. Up to now, a large number of dispersing methods and inks for Ink jet recording have been proposed in the art. For example, Japanese Patent Laid-Open No. 252467/1991 proposes an ink composition comprising water, a styrene/maleic acid copolymer, xcex5-caprolactam, and a pigment, and Japanese Patent Laid-Open No. 79680/1991 proposes an ink composition comprising an aqueous medium, a styrene/maleic acid copolymer, and a copper phthalocyanine pigment.
Further, for ink compositions comprising pigments as the colorant, a task to be accomplished is to improve the rubbing/scratch resistance of printed images. Specifically, unlike dyes penetrable into recording media, pigments stay on the surface of recording media, making it necessary to improve the rubbing/scratch resistance using some means.
When utilization of pigments as the colorant for inks for ink jet recording is considered, as compared with dyes, pigments have superior lightfastness and waterfastness, but on the other hand are smaller in number of kinds of usable colorants. in practical use of inks for ink jet recording, hue besides lightfastness and waterfastness should be sufficiently studied.
Furthermore, a proposal has been made for enhancing the penetration of the ink composition, shortening the drying time, and forming a large pixel (for example, a dot) using a smaller amount of the ink. In pigment-based ink compositions, however, no satisfactory penetration is often provided due to the relation with the pigments and other ingredients.
Further, in recent years, formation of color images by ink jet recording using a plurality of color ink compositions has been performed in the art. Color images are generally formed using three colors of a yellow ink composition, a magenta ink composition, and a cyan ink composition, and, in some cases, four colors of the above three color compositions plus a black ink composition. What is required of ink compositions for the formation of such color images is that they as such can exhibit good color development and, in addition, when used in combination with a plurality of ink compositions can develop good intermediate colors and black.
In such color images, the presence of even one color having poor lightfastness causes a change in hue of images which results in extremely deteriorated color image quality. Accordingly, more regulated lightfastness is required of color ink compositions. Among others, images printed by an ink jet recording printer are considered utilizable in various forms. In particular, for example, photograph-like prints are considered to be put as displays for a long period of time in places exposed to light from fluorescent lamps or places exposed to direct sunlight in the open and the like. For this reason, lightfastness is a very important property required of images formed by the ink jet recording method.
C.I. Pigment Yellow 74 has hitherto been extensively used as a colorant for yellow inks, This pigment exhibits much better yellow color development than other pigment-based colorants. For C.I. Pigment Yellow 74, however, there is room for further improvement in lightfastness.
On the other hand, realization of good images free from feathering or bleeding on recording media and, in addition, sure ejection through nozzles in an ink jet recording head without deviation from a predetermined droplet trajectory direction are required of ink compositions for ink jet recording. A failure of the ink to be ejected or ejection of ink droplets in a direction deviated from the predetermined ink droplet trajectory direction (the deviation of ink droplets from a predetermined ink droplet trajectory direction being hereinafter often referred to as xe2x80x9cink droplet trajectory directionality problemxe2x80x9d) results in dropouts, lowered sharpness of images, and other unfavorably phenomena. In order to prevent the failure of the ink to be ejected or the ink droplet trajectory problem, various proposals have been made on the regulation of the kind and amount of ingredients added to the ink composition. Further, several proposals have been made on the construction of an ink jet recording head which is less likely to cause the ink droplet trajectory directionality problem. For the latter, for example, a method has been proposed which imparts, to a nozzle plate, a property such that the nozzle plate is less likely to be wetted by the ink (ink-repellent properties) , thereby permitting ink droplets to be ejected surely and without any ink droplet trajectory directionality problem. For example, Japanese Patent Laid-Open No. 107848/1982 proposes that an ink-repellent coating of a fluororesin or the like is evenly formed by sputtering on the internal surface of nozzles and the surface of the nozzle plate to prevent the ink from being leaked from around the nozzles. Further, Japanese Patent Laid-Open No. 125220/1995 proposes the provision of an ink-repellent coating which extends to the internal surface of nozzles to such a predetermined extent as determined in a relationship with the amount of the ink in droplets.
The present inventors have now found that an ink set comprising a combination of color ink compositions respectively containing specific pigments can realize images having excellent color reproduction. The present inventors have further found that a combination of the color ink compositions with the ink jet recording method using an ink jet recording head provided with a nozzle plate described in Japanese Patent Laid-Open No. 125220/1995 can suppress the failure of the ink droplets to be ejected and the ink droplet trajectory directionality problem and can cope with high response frequencies. Furthermore, the present inventors have found that a yellow ink composition containing C.I. Pigment Yellow 128 can realize images having excellent color reproduction and lightfastness. The present invention has been made based on such finding.
Accordingly, it is an object of the present invention to provide a pigment-based ink set, a yellow ink composition containing C.I. Pigment Yellow 128, and image recording methods using the same, which can realize images having excellent color reproduction.
According to one aspect of the present invention, there is provided an ink set comprising at least a yellow ink composition, a magenta ink composition, a cyan ink composition, and a black ink composition,
said yellow ink composition comprising C.I. Pigment Yellow 128 as a colorant,
said magenta ink composition comprising C.I. Pigment Red 122 as a colorant,
said cyan ink composition comprising C.I. Pigment Blue 15: 3 as a colorant,
said black ink composition comprising carbon black as a colorant.
According to a further aspect of the present invention, there is provided a yellow ink composition comprising: 1 to 5% by weight of C.I. Pigment Yellow 128; a water-soluble resin based on styrene-(meth)acrylic acid; 0.1 to 30% by weight of glycerin; 1 to 20% by weight of triethylene glycol monobutyl ether; 0.1 to 5% by weight of an acetylene glycol; and a water-soluble organic solvent.